Method for producing alkanolamines

ABSTRACT

At least one alkanolamine is prepared by reacting ammonia with alkylene oxide in a reaction space in the presence of a catalyst to give monoalkanolamine or dialkanolamine or trialkanolamine or a mixture of two or three of these compounds, the distribution of the various alkanolamines within the product spectrum being controlled by means of the temperature in the reaction space, by a process in which the temperature is established by regulating the temperature profile in the reaction space.

[0001] The present invention relates to a process for the preparation ofalkanolamines from alkylene oxide and ammonia, the novel process beingdistinguished by the fact that the selectivity of the reaction can beinfluenced by specifically controlling the temperature of the reactionspace, this control being effected by regulating the temperature profilein the reaction space. In a particularly preferred embodiment, thepresent invention relates to a process for carrying out the reactionflexibly in the preparation of alkanolamines, which process isdistinguished by the fact that the product selectivities of thealkanolamine synthesis can be established by the above mentioned measureof specific temperature regulation in a reaction space in the presenceof the same catalyst. In an embodiment which is likewise preferred, thepresent invention relates to a process for the preparation ofdialkanolamines, in which monoalkanolamine is prepared selectively in afirst process stage and dialkanolamine is prepared selectively from thismonoalkanolamine in a second process stage.

[0002] DE-A 19 41 859.8 describes a process for the selective synthesisof monoalkanolamines from alkylene oxide and ammonia in the presence ofa cation-exchange resin. For optimum utilization of the plant, thetemperature of the reaction volume of the catalyst and the flow rate ofthe reaction mixture through the catalyst are established so that thehighest yields of monoalkanolamine per unit time can be achieved.

[0003] EP-A 0 652 207 discloses a process for the preparation ofmonoalkanolamines from alkylene oxides and ammonia in the liquid phase,the catalyst used being one which comprises a rare earth element whichis applied to a heat-resistant support. For example, the preparation ofmonoethanolamine is described explicitly. The temperature at which thereaction takes place is determined only by the temperature of the oilbath, as is evident from the examples.

[0004] EP-A 0 941 986 describes a process for the preparation ofdialkanolamines starting from alkylene oxide and ammonia, zeolitecatalysts being used. Here too, the temperature at which the reactiontakes place is only determined roughly via the temperature of the oilbath.

[0005] DD 298 636 describes a process for the preparation ofdiethanolamine by reacting ammonia and ethene oxide in the gas phase,the catalyst used being a heterogeneous catalyst, a crystalline silicateof the pentasil type.

[0006] DE-A 25 47 328 describes a process for the continuous preparationof dialkanolamines, in which, in a first reaction zone, an olefin oxideis brought into contact with ammonia, the monoalkanolamine formed isseparated from the material removed from the first reaction zone and themonoalkanolamine separated off is brought into contact in a secondreaction zone with an olefin oxide. The trialkanolamine preparation isregulated by establishing the molar ratio of monoalkanolamine to olefinoxide, and the reactions take place with exclusion of water in theabsence of a catalyst.

[0007] It is an object of the present invention to provide a processwhich makes it possible to establish and to control the productselectivity very exactly and hence to have a process which, inter alia,can be adapted flexibly and rapidly to a specific product demand and/orpermits high product selectivities.

[0008] We have found that this object is achieved by a process for thepreparation of at least one alkanolamine by reacting ammonia withalkylene oxide in a reaction space in the presence of a catalyst to givemonoalkanolamine or dialkanolamine or trialkanolamine or a mixture oftwo or three of these compounds, the distribution of the variousalkanolamines in the product spectrum being controlled by means of thetemperature in the reaction space, wherein the temperature isestablished by regulating the temperature profile in the reaction space.

[0009] In the context of the present invention, the term reaction spacedenotes reactors, reactor compartments and reactor sections. Anindividual reactor can therefore constitute both a single reaction spaceand, if this individual reactor is divided into two or more sections, ifnecessary sections or compartments physically separated from oneanother, for process engineering reasons, two or more different reactionspaces. The term reaction space also includes those embodiments in whichtwo or more reactors, for example connected in parallel or in series,constitute a single reaction space.

[0010] The regulation of the temperature profile in the reaction spacecan be carried out by all suitable methods. For example, it is possibleto start from a specific setpoint value of the temperature profile, theactual value determined by suitable methods being compared with thissetpoint value and the actual value being adapted iteratively ordirectly, discretely or continuously, to this setpoint value by suitablemethods. It is also possible to change the setpoint value of thetemperature profile taking into account, for example, the productspectrum obtained and to adapt the actual value to the respectivedifferent setpoint values and hence to variable setpoint values. In thecontext of the present application, the term setpoint value denotes thatvalue of the temperature profile for which a specific desireddistribution of the alkanolamines in the product spectrum is obtained.In the context of the present application, the term actual value denotesthat value of the temperature profile which is determined by suitablemethods and is adapted to the setpoint value. In the context of thepresent application, the term value of the temperature profile denotesthe totality of the measured values which are determined by suitablemethods of measurement and establish the temperature profile in thereaction space.

[0011] The temperature or the temperature profile is regulatedessentially by adapting the heat flows from the reaction space into theinsulation means surrounding the reaction space, for example adouble-jacket cooling tube surrounding the reaction space. In thisembodiment, as also stated below, a plurality of double-jacket coolingtubes are more preferably used in succession along the reaction space,for example a tubular reactor. These are loaded independently of oneanother with cooling liquid. This arrangement facilitates the flexiblecontrol of the temperature profile. For a specific reactor design andreactant flows of fixed compositions, control parameters are the volumeflow rates of the coolant and the inlet temperatures in the insulationmeans, for example the double jacket, or into the successive doublejackets around the reactor.

[0012] The variable flow rate of the coolant is realized, for example,by controlling corresponding circulation pumps. The differenttemperature of the coolant on entering the insulation means can bevaried within wide limits by means of one or more secondary circulationshaving heat exchangers.

[0013] The temperature profile in the reaction space can be obtained ingeneral by any suitable method. In particular, the number and positionof the measuring points at which the temperature is determined can beadapted to the geometry and size of the reaction space. In this context,the temperature profile in the reaction space can therefore bedetermined with any desired accuracy corresponding to the requirements.

[0014] The temperature measurements per se can be carried out here byany suitable method.

[0015] For the temperature measurement, all conventional temperaturesensors can be used in the interior of the reaction space, it beingpossible to use, for example, thermocouples or resistance thermometerswith or without a protective tube. For the temperature measurement atthe inlet and outlet of the cooling medium in the insulation means,sensors of the same type are preferably used. In addition, optical,contactless methods for measuring the heat radiation can be used at theouter limit of the insulation means for the temperature measurement orthe measurement can be effected by means of thermocouples or resistancethermometers by a contact method at the outer limit of the insulationmeans. Preferably, the temperature measurement is carried out in theinterior of the reaction space in thermal protective tubes. The sensorsused are either thermocouples or resistance thermometers, depending onthe process control system.

[0016] In the process according to the invention, particularly preferredmeasured variables for temperature control are the temperature gradientand that location in the reaction space at which the maximum temperatureis reached. In this context, the term temperature gradient is understoodas meaning the temperature difference between the maximum temperature inthe reactor and the temperature of the starting material stream or ofthe starting material streams. Accordingly, if two or more startingmaterial streams at different temperatures are passed into the reactionspace, it is possible that, starting from a maximum temperature, two ormore different temperature gradients are used for temperature control.Depending on the geometry and/or size of the reaction space, it is alsopossible that there are in the reaction space two or more locations atwhich in each case the same maximum temperatures occur within theaccuracy of measurement and/or the accuracy requirements of theprocedure.

[0017] Regarding the stress on the material of the reactor, it isparticularly advantageous not to use a particularly hot reaction zonewhich is sharply limited spatially but a balanced temperature gradientover the length of the tube. In addition, the choice of the hotspottemperature and of the location of the hotspot along the desired ratioof the products is advantageous. They are obtained from the choice ofthe volume flow rates (residence times) and the temperature level thusestablished in the reactor.

[0018] The present invention therefore also relates to a process, asdescribed above, wherein the regulation of the temperature profile inthe reaction space is effected by establishing the temperature gradientin the reaction space in a controlled manner or by establishing thelocation of the maximum temperature in the reaction space in acontrolled manner or by establishing both parameters in a controlledmanner.

[0019] The temperature gradient describes the local change in thetemperature along the reaction zone. For this purpose, a plurality oftemperature sensors are distributed along this zone in the reactionspace. With said sensors, the local change in the temperature and itsmaximum value, the hotspot, can be determined, regulation being effectedas described further above herein.

[0020] The temperature profile which occurs and is regulated in thereaction space in the novel process can be influenced by all suitablemeasures.

[0021] For example, the heat generated in the course of the reaction canbe removed by any suitable method in order to reduce the temperature.Inter alia, external cooling, for example by one or more cooling jacketswhich surround the reaction space, is possible. It is also possible toremove the evolved heat of reaction by passing one or more suitableinert gases through the reaction space. Heat of reaction can also beremoved, for example, by evaporating a part of the ammonia present inthe reaction space. All suitable methods can likewise be used forincreasing the temperature in the reaction space. These include bothdirect methods, for example heating the reaction space from outside, andindirect methods. Indirect methods are understood as meaning, interalia, those methods in which a temperature increase is achieved bycomplete or partial reduction of the temperature-reducing measuresdescribed above.

[0022] If necessary for regulating the temperature profile in the novelprocess, the temperature can be increased in one or more sections andthe temperature can be simultaneously reduced in one or more sections,depending on the geometry of the reaction space.

[0023] Further possibilities for influencing the temperature in thereaction space are by means of the residence time of the reactants inthe reaction space, the flow rate of the reaction mixture through thereaction space in a continuous procedure or the temperature of thestarting material stream or of the starting material streams which arepassed into the reaction space.

[0024] Preferably, the temperature profile is determined by theliberated chemical energy with corresponding heating-up of the reactantstream and regulated by physical heat removal by radiation or moreeffectively by heat removal by means of a cooling medium. For thispurpose, reference is also made to the above detailed descriptionrelating to the specific control of the heat removal using a coolingmeans which makes it possible to control the heat removal within widelimits.

[0025] The group of reactants as used above includes all compounds whichreact with one another in the course of the novel process. These are inparticular alkylene oxide, ammonia and alkanolamine. Further examplesare monoalkanolamine, which can react with alkylene oxide to givedialkanolamine, and dialkanolamine, which can react with alkylene oxideto give trialkanolamine.

[0026] Of course, all these measures can also be combined with oneanother in a suitable manner. An example of a further method, which canlikewise be combined with the abovementioned measures, involves themolar ratio of the starting materials ammonia and alkylene oxide. Inthis very particularly preferred embodiment of the novel process, thedistribution of the various alkanolamines in the product spectrum isaccordingly controlled by the molar ratio of the starting materials ofthe reaction which are passed into the reaction space.

[0027] The present invention also relates to a process, as describedabove, wherein the distribution of the various alkanolamines in theproduct spectrum is additionally controlled through the molar ratio ofammonia to alkylene oxide.

[0028] It is also possible in principle to influence the distribution ofthe various alkanolamines in the product spectrum additionally by meansof the pressure under which the reaction is carried out.

[0029] In general, there are no restrictions with regard to the geometryand the size of the reaction space. For example, it is possible inparticular to use stirred kettles, stirred kettle cascades, tubularreactors, tubular reactor cascades or reactive distillation columns assuitable reaction spaces. Moreover, both batchwise and continuousprocedures are possible. Combinations of batchwise and continuousprocedures and combinations of different reactor forms, which in turncan be connected in series and/or in parallel, are also possible.

[0030] In a particularly preferred embodiment of the novel process,tubular reactors are used for reacting alkylene oxide with ammonia. Inthis context, two or more tubular reactors may be connected in series ortwo or more tubular reactors can be connected in parallel or acombination of serial and parallel arrangements may be provided.

[0031] The present invention therefore also relates to a process, asdescribed above, wherein the reaction is carried out in a tubularreactor.

[0032] The tubular reactor used according to the invention is, forexample, a pressure-resistant reaction tube which can be dividedlogically or physically into individual sections. The sections arethermostated either together or individually, independently of oneanother, for example by coolant circulations surrounding them, i.e. by,for example, double-jacket tubes or other constructive measuresdetermining the heat flow. In the individual sections, the temperatureis determined by a plurality of temperature sensors, i.e. at least twotemperature sensors.

[0033] The constructional arrangement of the sections can also berealized in a manner such that the reaction mixture flows successivelythrough a plurality of reaction tubes arranged concentrically one insidethe other so that the heat removed is transferred not only to thecooling medium in the surrounding double-jacket tubes but also orinstead serves for heating the reaction mixture itself.

[0034] The reaction as such is carried out in general in the presence ofa catalyst.

[0035] The use of a homogeneous catalyst, for example water or analkanolamine, is generally possible. Inter alia, suitable inorganic ororganic acids or ammonium salts may be mentioned here.

[0036] In the novel process, a heterogeneous catalyst is particularlypreferably used. Of course, two or more suitable heterogeneous catalystsmay also be used. Furthermore, zeolite-analogous materials, for examplealuminophosphates and silicoaluminophosphates, and organic ionexchangers, as described, for example, in DE-A 19 41 859.8, can be used.

[0037] In a very particularly preferred embodiment, a zeolite catalystis used as the one or more heterogeneous catalysts. In the context ofthe present invention, the term zeolite catalyst denotes all oxideswhich are suitable as catalysts and have or comprise a zeolite structureor a zeolite-analogous structure.

[0038] The present invention therefore also relates to a process, asdescribed above, wherein the reaction is carried out in the presence ofa heterogeneous catalyst, preferably of a heterogeneous zeolitecatalyst.

[0039] The catalyst preferably used according to the invention ispreferably an oxide, comprising at least the elements Si and Ti, atleast noncrystalline silica and at least one crystalline silicate phasewhich has at least one zeolite structure, noncrystalline silica beingapplied to at least one crystalline silicate phase which has at leastone zeolite structure, wherein the oxide has no silicon-carbon bonds.

[0040] Zeolites as such are known to be crystalline aluminosilicateshaving ordered channel and cage structures which have micropores. Theterm micropores as used in the context of the present inventioncorresponds to the definition in Pure Appl. Chem. 57 (1985), 603-619,and denotes pores having a pore diameter of less than 2 nm. The networkof such zeolites is composed of SiO₄ and AlO₄ tetrahedra which arelinked by common oxygen bridges. An overview of the known structures isto be found, for example, in W. M. Meier, D. H. Olson and Ch. Baerlocherin Atlas of Zeolite Structure Types, Elsevier, 4th Edition, London 1996.

[0041] There are in particular zeolites which contain no aluminum and inwhich some of the Si(IV) in the silicate lattice has been replaced bytitanium as Ti(IV). The titanium zeolites, in particular those having acrystal structure of the MFI type, and possibilities for theirpreparation are described, for example, in EP-A 0 311 983 or EP-A 0 405978.

[0042] It is known that titanium zeolites having an MFI structure can beidentified by means of a specific pattern in the determination of theirX-ray diffraction patterns and additionally by means of a skeletalvibration band in the infrared region (IR) at about 960 cm⁻¹ and thusdiffer from alkali metal titanates or crystalline and amorphous TiO₂phases.

[0043] Specific examples of the catalysts preferably used in the novelprocess are zeolites having a pentasil structure, in particular thosehaving structures ABW, ACO, AEI, AEL, AEN, AET, AFG, AFI, AFN, AFO, AFR,AFS, AFT, AFX, AFY, AHT, ANA, APC, APD, AST, ATN, ATO, ATS, ATT, ATV,AWO, AWW, BEA, BIK, BOG, BPH, BRE, CAN, CAS, CFI, CGF, CGS, CHA, CHI,CLO, CON, CZP, DAC, DDR, DFO, DFT, DOH, DON, EAB, EDI, EMT, EPI, ERI,ESV, EUO, FAU, FER, GIS, GME, GOO, HEU, IFR, ISV, ITE, JBW, KFI, LAU,LEV, LIO, LOS, LOV, LTA, LTL, LTN, MAZ, MEI, MEL, MEP, MER, MFI, MFS,MON, MOR, MSO, MTF, MTN, MTT, MTW, MWW, NAT, NES, NON, OFF, OSI, PAR,PAU, PHI, RHO, RON, RSN, RTE, RTH, RUT, SAO, SAT, SBE, SBS, SBT, SFF,SGT, SOD, STF, STI, STT, TER, THO, TON, TSC, VET, VFI, VNI, VSV, WEI,WEN, YUG, ZON or a mixed structure comprising two or more of thesestructures and ITQ-4, ITQ-6, ITQ-7 and CIT-6. A large number of thesezeolites of this type are described, for example, in the abovementionedpublication by Meier et al.

[0044] The oxide used according to the invention as a catalyst mayfurthermore comprise titanium-containing zeolites having the UTD-1,CIT-1, CIT-5, MCM-22 or MCM-61 structure. Examples of furthertitanium-containing zeolites are those having the ZSM-48 or ZSM-12structure. Such zeolites are described, inter alia, in U.S. Pat. No.5,430,000 and WO 94/29408, the content of which in this context ishereby included by reference in its entirety in the present application.In the context of the present invention, Ti zeolites having the MFI, MELor MFI/MEL mixed structure are to be regarded as being particularlypreferred. Ti zeolites having a skeletal structure isomorphous withbeta-zeolite may also be mentioned as being preferred.

[0045] In addition to silicon and titanium, the one or more crystallinesilicate phases having at least one zeolite structure may also containadditional elements, e.g. aluminum, zirconium, vanadium, tin, zinc,iron, tellurium, niobium, tantalum, chromium, cobalt, nickel, gallium,germanium, boron or small amounts of fluorine.

[0046] Preferably, the novel oxide comprises titanium, vanadium,chromium, niobium and zirconium zeolites, more preferably titaniumzeolites and in particular titanium silicalites.

[0047] Regarding the pore structure of the one or more crystallinesilicate phases having a zeolite structure, there are no particularrestrictions in this context. For example, structures having micropores,mesopores or macropores or having micropores and mesopores or havingmicropores and macropores or having micropores and mesopores andmacropores are possible, the definition of these pores in the context ofthe present invention corresponding to the definition in Pure Appl.Chem. 45, 71 et seq. and characterizing micropores having a diameter ofless than or equal to 2 nm, mesopores having a diameter greater than 2nm to about 50 nm and macropores having a diameter of greater than 50nm.

[0048] Regarding the preparation process for the novel oxide, there areessentially no restrictions provided that the novel oxide is obtainedfrom this process. Preferably, the oxide is prepared in a process inwhich a suitable oxidic material which has at least one crystallinesilicate phase having a zeolite structure is treated with a suitablesilane or silane derivative.

[0049] The present invention therefore also relates to a process, asdescribed above, wherein the catalyst is a silylated zeolite catalyst.

[0050] This catalyst is preferably obtained by a process for thepreparation of an oxide comprising at least the elements Si and Ti, atleast noncrystalline silica and at least one crystalline silicate phase,in which

[0051] (a) an oxidic material comprising at least the elements Si and Tiand at least one crystalline silicate phase which has at least onezeolite structure is prepared and

[0052] (b) the oxidic material obtained from (a)

[0053] (i) is reacted, in at least one solvent, with at least one silaneor at least one silane derivative or with a mixture of two or morethereof to give a mixture comprising at least one oxidic reactionproduct and the one or more solvents,

[0054] the one or more solvents are removed from the mixture directlyafter the reaction, to give the one or more oxidic reaction products,and

[0055] the one or more oxidic reaction products are calcined directlyafter the removal of the one or more solvents, to give the oxide, or

[0056] (ii) are reacted in the gas phase with at least one silane or atleast one silane derivative or a mixture of two or more thereof to giveat least one oxidic reaction product and the one or more oxidic reactionproducts are calcined directly after the reaction, to give the oxide.

[0057] Details of this process appear in DE-A 199 54 322.4, which ishereby incorporated by reference in the context of the presentapplication.

[0058] In a preferred embodiment, the one or more silanes or the one ormore silane derivatives are selected from the group consisting oftrichlorosilane, silicon tetrachloride, methylhydrogendichlorosilane,mono-, di- and trimethylchlorosilane, tetraalkyl orthosilicates havingidentical or different alkyl radicals of more than 2 carbon atoms,hydrolysis products of these tetralkyl orthosilicates,alkylalkoxysilanes having identical or different alkyl radicals andalkoxy radicals, and the abovementioned silanes or silane derivativeswhich additionally have one or more functional groups selected from thegroup consisting of hydroxyl, carboxyl, vinyl, glycidyl, amino andaminoalkyl groups.

[0059] Particularly preferred in the context of the present inventionare those silanes or silane derivatives which have at least onesilicon-carbon bond. The one or more silanes or the one or more silanederivatives are therefore preferably selected from the group consistingof methylhydrogendichlorosilane, mono-, di- and trimethylchlorosilane,tetraalkyl orthosilicates having identical or different alkyl radicalsof more than 2 carbon atoms, hydrolysis products of these tetraalkylorthosilicates, alkylalkoxysilanes having identical or different alkylradicals and alkoxy radicals, and the abovementioned silanes or silanederivatives, which additionally have one or more functional groupsselected from the group consisting of hydroxyl, carboxyl, vinyl,glycidyl, amino and aminoalkyl groups.

[0060] Also very particularly preferably, an oxidic material in the formof a molding, produced from titanium silicalite having the TS-1structure and a silica binder, is reacted with3-aminopropyltriethoxysilane, dissolved in a suitable anhydrous solvent.

[0061] Preferably, the novel catalyst is used in a fixed bed. Stacked orstructured packing and thin-film catalysts are other examples of formswhich may be used.

[0062] This novel, preferably used heterogeneous zeolite catalyst can beregenerated in the novel process generally by any suitable method. Suchmethods are described, for example, in DE-A 100 15 246.5, which ishereby incorporated by reference in the context of the presentapplication.

[0063] In general, all suitable alkylene oxides may be used in the novelprocess, in particular those having the structure R₁R₂COCR₃R₄ beingpreferred. Here, R₁ to R₄ are identical or different and are eachhydrogen, methyl or ethyl. Alkylene oxides of 2 to 4 carbon atoms areparticularly preferably used, ethylene oxide in turn being preferablyused.

[0064] The present invention therefore also relates to a process, asdescribed above, wherein the alkylene oxide used is ethylene oxide.

[0065] Here, the alkylene oxide can be prepared in principle by anysuitable process and used in the novel process. Such processes are partof the prior art and are described in detail, inter alia, in Ullmann'sEnzyclopädie der Technischen Chemie (5th Edition). Furthermore,reference is made to the preparation processes for alkylene oxide and inparticular for propylene oxide, as described, inter alia, inPCT/EP99/05740 and DE-A 100 15 246.5, which is hereby incorporated byreference in its entirety in the context of the present application.

[0066] In a preferred embodiment, the alkylene oxide used according tothe invention as starting material is prepared by reacting thecorresponding alkene with a hydroperoxide, oxygen-containing gas or pureoxygen.

[0067] The present invention therefore also relates to a process, asdescribed above, wherein the alkylene oxide is prepared by reacting analkene with a hydroperoxide.

[0068] If, for example, propylene oxide is used as a starting material,it is preferably prepared by reacting propene with hydrogen peroxide.The reaction with hydrogen peroxide is more preferably effected in thepresence of a catalyst, preferably of a heterogeneous catalyst, morepreferably of a catalyst which has a zeolite structure. Regarding thepossible zeolite structures, reference may be made to the structuresdescribed above. An example of a particularly preferred catalyst is onehaving the structure TS-1. In this context, reference is made to theabove-mentioned publications PCT/EP99/05740 and DE-A 100 15 246.5.

[0069] Regarding the preparation of the preferably used ethylene oxide,reference is made to Ullmann's Encyclopadie der Technischen Chemie (loc.cit.).

[0070] If monoalkanolamine is preferably to be prepared in the novelprocess, the product stream from the reaction space, which may containdialkanolamine and/or trialkanolamine and ammonia and water in additionto the monoalkanolamine, can be fed to one or more separation stages inwhich this mixture is separated. In a preferred embodiment, first thelow-boiling components, for example ammonia and water, are separated offand then, if required, the monoalkanolamine is separated fromdialkanolamine and/or trialkanolamine, preferably by distillation. Here,the distillation can be carried out by any suitable method.

[0071] The mono-, di- and triethanolamines can be separated off byconventional methods. Distillation is preferred, but liquid/liquidextraction or separations by membrane are also used.

[0072] The components separated off, such as ammonia or water, can thenbe recycled to the process in which monoalkanolamine is preferablyprepared. Monoalkanolamine separated off can be obtained as a desiredproduct or can be wholly or partly fed to a process in which di- ortrialkanolamine is preferably prepared and in which the monoalkanolamineserves as a starting material.

[0073] If dialkanolamine is preferably prepared in the novel process,the product stream from the reaction space, which may containmonoalkanolamine and/or trialkanol-amine and ammonia and water inaddition to the dialkanolamine, can be fed to one or more separationstages in which this mixture is separated. In a preferred embodiment,once again first the low-boiling components, for example ammonia andwater, are separated off and then, if required, the dialkanolamine isseparated from monoalkanolamine and/or trialkanolamine, preferably bydistillation. Here, the distillation can once again be effected by anysuitable method.

[0074] The components separated off, such as monoalkanolamine, ammoniaor water, can then be recycled to the process in which dialkanolamine ispreferably prepared. Dialkanolamine separated off can be obtained as adesired product or can be fed wholly or partly to a process in whichtrialkanolamine is preferably prepared and in which the dialkanolamineserves as a starting material.

[0075] If trialkanolamine is preferably prepared in the novel process,the product stream from the reaction space, which may containmonoalkanolamine and/or dialkanol-amine and ammonia and water inaddition to trialkanolamine, can be fed to one or more separation stagesin which this mixture is separated. In a preferred embodiment, onceagain first the low-boiling components, for example water and ammonia,are separated off and then, if required, the trialkanolamine isseparated from monoalkanolamine and/or dialkanolamine, preferably bydistillation. Here once again, the distillation can be effected by anysuitable method.

[0076] The components separated off, such as monoalkanolamine,dialkanolamine, ammonia or water, can then be recycled to the process inwhich trialkanolamine is preferably prepared. Monoalkanolamine separatedoff can also be fed to a further process in which dialkanolamine ispreferably prepared and in which the monoalkanolamine serves for astarting material.

[0077] The mono-, di- and triethanolamines can be separated off byconventional methods. Distillation is preferred but liquid/liquidextraction or separations through membranes are also used.

[0078] An advantage of the novel control of the distribution of thevarious alkanolamines in the product spectrum by regulating thetemperature profile in the reaction space is, inter alia, that theprocess can be designed to be substantially more flexible than theprocesses described in the prior art. Whereas in the prior art theprocesses or the catalysts described in this context were optimized sothat either monoalkanolamine or dialkanolamine or trialkanolamine can beprepared in a specific yield, the novel process permits, through thespecific temperature regulation inter alia, preferably in combinationwith the regulation of the molar ratio of the starting materials ammoniaand alkylene oxide, a procedure in which mono- or di- or trialkanolamineis first preferably prepared in a single reaction space in the presenceof the same catalyst in a first process stage and an alkanolamine whichis different from the alkanolamine preferably prepared in the firstprocess stage is preferably prepared in a second process stage throughthe novel regulation.

[0079] By means of this flexible procedure, it is possible, for example,to respond in a variable manner to customers' wishes or to adapt theprocess to changing market conditions without great expense.

[0080] The present invention therefore also relates to a process,described above, wherein

[0081] (i) in a first process stage, monoalkanolamine or dialkanolamineor trialkanolamine is selectively prepared and

[0082] (ii) in a second process stage in the same reaction space and inthe presence of the same catalyst, by regulation of the temperatureprofile in the reaction space and, if required, additionally through themolar ratio of ammonia to alkylene oxide, the product selectivity in thesecond process stage is changed in comparison with the first processstage.

[0083] Of course, this embodiment of the process also comprisesprocedures in which, in at least one additional process stage, likewisein the same reaction space and likewise in the presence of the samecatalyst, by regulation of the temperature profile in the reaction spaceand, if required, additionally through the molar ratio of ammonia toalkylene oxide, the product selectivity in this at least one additionalprocess stage is changed in comparison with the second or generally withthe respective preceding process stage.

[0084] Further possibilities for likewise influencing the distributionof the various alkanolamines in the product spectrum by additionalmeasures are described above and can also be used in the flexibleprocess described here.

[0085] In the novel process, monoalkanolamines are generally prepared atfrom 20 to 250, preferably from 40 to 230, particularly preferably from70 to 160, bar. The temperature of the ammonia stream as well as thetemperature of the alkylene oxide stream, which are passed into thereaction space, is in general from 20 to 200° C., preferably from 50 to150° C., particularly preferably from 60 to 140° C. Here, the molarratio of ammonia to alkylene oxide is in general from 100 to 7,preferably from 40 to 7, particularly preferably from 20 to 7. Themaximum temperature in the reaction space is furthermore generally lessthan 200° C., preferably from 20 to 180° C., more preferably from 50 to150° C., particularly preferably from 60 to 130° C.

[0086] In the novel process, dialkanolamines are generally prepared atfrom 20 to 250, preferably from 40 to 230, particularly preferably from70 to 160, bar. The temperature of the ammonia stream as well as thetemperature of the alkylene oxide stream, which are passed into thereaction space, is in general from 20 to 180° C., preferably from 40 to150° C., particularly preferably from 60 to 140° C. Here, the molarratio of ammonia to alkylene oxide is in general from 10 to 2,preferably from 8 to 2, particularly preferably from 7 to 2. The maximumtemperature in the reaction space is furthermore generally from 70 to200° C., preferably from 75 to 150° C., particularly preferably from 80to 140° C.

[0087] In the novel process, trialkanolamines are generally prepared atfrom 5 to 250, preferably from 30 to 230, particularly preferably from40 to 160, bar. The temperature of the ammonia stream as well as thetemperature of the alkylene oxide stream, which are passed into thereaction space, is generally from 20 to 180° C., preferably from 40 to150° C., particularly preferably from 60 to 140° C. Here, the molarratio of ammonia to alkylene oxide is in general from 10 to 0.3,preferably from 8 to 0.3, particularly preferably from 6 to 0.3. Themaximum temperature in the reaction space is furthermore generally lessthan 400° C., more preferably from 75 to 400° C., even more preferablyfrom 90 to 400° C., particularly preferably from 100 to 400° C.

[0088] This procedure can be carried out essentially for all alkyleneoxides which are described above and can be used as starting materials.For the purposes of the present invention, a preferably used startingmaterial is ethylene oxide.

[0089] The present invention therefore relates to a process, asdescribed above, wherein

[0090] (i) in a first process stage, monoethanolamine or diethanolamineor triethanolamine is selectively prepared and

[0091] (ii) in a second process stage, in the same reaction space and inthe presence of the same catalyst, by regulation of the temperatureprofile in the reaction space and, if required, additionally through themolar ratio of ammonia to ethylene oxide, the product selectivity in thesecond process stage is changed in comparison with the first processstage.

[0092] In connection with this preferred embodiment of the novelprocess, in which, in a first process stage, monoethanolamine ordiethanolamine or triethanolamine is selectively prepared and, in asecond process stage, in the same reaction space and in the presence ofthe same catalyst, by regulation of the temperature profile in thereaction space and, if required, additionally through the molar ratio ofammonia to ethylene oxide, the product selectivity in the second processstage is changed in comparison with the first process stage, the termselectivity is used as follows:

[0093] the desired product monoethanolamine is selectivity prepared whenmore than 65% by weight of monoethanolamine are present in the productspectrum;

[0094] the desired product diethanolamine is selectively prepared whenmore than 35% by weight of diethanolamine are present in the productspectrum;

[0095] the desired product triethanolamine is selectively prepared whenmore than 35% by weight of triethanolamine are present in the productspectrum.

[0096] The data in % by weight are based in each case on the totalamount of the ethanolamines prepared.

[0097] Accordingly, the present invention also relates to a process, asdescribed above, wherein

[0098] (a) more than 65% by weight of monoethanolamine are formed in (i)and more than 35% by weight of di- or triethanolamine are formed in (ii)or

[0099] (b) more than 35% by weight of di- or triethanolamine are formedin (i) and more than 65% by weight of monoethanolamine are formed in(ii),

[0100] based in each case on the total amount of mono-, di- andtriethanolamine.

[0101] Regarding the novel procedure, it should be noted that thepressure is chosen at least so that the fluid reaction mixture ispresent as a single phase without the presence of a gas phase. On thebasis of thermodynamics, the resulting minimum pressure is the vaporpressure of the reaction mixture at the corresponding temperature, i.e.said minimum pressure is determined by the concentration of thecomponents and the temperature in individual reactor section.

[0102] It is advantageous, but not essential, that the reactor beoperated at a single pressure in its total volume. Otherwise, forexample, sections with decreasing system pressure are possible and easyto realize, the minimum pressure being determined by thermodynamics, forexample by the concentration of the lowest-boiling components in thereaction mixture at the temperature of the hotspot.

[0103] If monoethanolamine is prepared in the novel process, for examplein a first process stage, in general a pressure of from 20 to 250,preferably from 40 to 230, particularly preferably from 70 to 160, baris employed. The residence times of the reaction medium in the reactorare in general from 2 to 60, preferably from 5 to 20, minutes. The molarratio of ammonia to ethylene oxide is in general from 5 to 100,preferably from 5 to 40, more preferably from 5 to 20, mol. Here,temperature gradients, i.e. temperature differences between maximumtemperature in the reaction space and the temperature of the unmixedstarting materials, which are in the range of, in general, from 0 to100° C., preferably from 0 to 80° C., more preferably from 0 to 30° C.,are employed.

[0104] If diethanolamine is to be selectively prepared in the secondprocess stage in the same reaction space in the presence of the samecatalyst, temperature gradients which are in the range of, in general,from 50 to 120° C., preferably from 60 to 100° C., are employed in thepressure ranges and residence time ranges which are chosen in the caseof the preparation of monoethanolamine.

[0105] If triethanolamine is to be selectively prepared in the secondprocess stage in the same reaction space in the presence of the samecatalyst, temperature gradients which are in the range of, in general,from 70 to 300° C. are employed in the pressure ranges and residencetime ranges which are chosen in the case of the preparation ofmonoethanolamine and/or of diethanolamine.

[0106] The reactions described here, using the stated reactionparameters, relate to the non-back-mixing tubular reactors preferablyused according to the invention but may also be applied or transferredto stirred kettles or arrangements of stirred kettles into stirredkettle cascades, which can likewise be used.

[0107] Of course, the novel process is not restricted to embodiments inwhich the reaction is carried out in a single reaction space. Rather,the control of the distribution of the various alkanolamines in theproduct spectrum by regulation of the temperature profile in thereaction space can be applied to all possible procedures. These alsoinclude processes in which an alkanolamine is prepared in a firstprocess stage in a first reaction space in the presence of a firstcatalyst by reacting an alkylene oxide with ammonia and the alkanolamineobtained is further reacted in a second process stage in a secondreaction space. Furthermore, a third process stage and very generallyany desired number of further process stages may also follow the secondprocess stage.

[0108] Regarding the further reactions, in the second or a furtherprocess stage, of the alkanolamine prepared according to the inventionin the first process stage, all reactions to which the alkanolamine canbe subjected are generally possible.

[0109] Preferred procedures of the novel process include those in whichan alkylene oxide is reacted with ammonia to give monoalkanolamine in afirst process stage in a first reaction space in the presence of a firstcatalyst and the monoalkanolamine obtained in the first process stage isreacted with alkylene oxide in a second process stage in a secondreaction space to give the dialkanolamine and/or to give thetrialkanolamine. Here, the monoalkanolamine can be reacted in the secondprocess stage with the same alkylene oxide which was used in the firstprocess stage. In this way, it is possible to prepare symmetrical di- ortrialkanolamines. The monoalkanolamine can also be reacted in the secondprocess stage with an alkylene oxide which is different from thealkylene oxide used in the first process stage. If, for example, anasymmetrical dialkanolamine is accordingly prepared in a second processstage, it can in turn be reacted in a third process stage with analkylene oxide which is identical to or different from one of thealkylene oxides used in the first and/or second process stage. It isalso possible to prepare, for example, symmetrical dialkanolamine in thefirst process stage and to react it with alkylene oxide in a secondprocess stage, the alkylene oxide used in the second process stage beingidentical to or different from the alkylene oxide used in the firstprocess stage. While it is possible in principle to work without acatalyst in the second process stage, it is particularly preferable tocarry out the reaction in the presence of a second catalyst which isidentical to or different from the catalyst used in the first processstage.

[0110] In a particularly preferred embodiment of the novel process,monoalkanolamine is prepared by reacting alkylene oxide with ammonia ina first process stage in a first reaction space in the presence of afirst catalyst. The monoalkanolamine thus obtained is separated from theproduct mixture and is reacted in a second process stage with thealkylene oxide, which was also used in the first process stage, to givedialkanolamine.

[0111] The present invention therefore also relates to a process, asdescribed above, which is referred to below as process II and wherein

[0112] (I) monoalkanolamine is selectively prepared by reacting ammoniawith alkylene oxide in a first process stage in a first reaction spacein the presence of a first catalyst, a mixture comprisingmonoalkanolamine being obtained,

[0113] (II) monoalkanolamine is separated, in a separation stage, fromthe mixture obtained from (I), and

[0114] (III) dialkanolamine is selectively obtained in a second processstage by reacting the monoalkanolamine obtained from (II) with ethyleneoxide in a second reaction space in the presence of a second catalyst.

[0115] The control of the distribution of the various alkanolamines inthe product spectrum by the novel regulation of the temperature profilein the reaction space can be effected here either in (I) or in (III) orin (I) and (III). Preferably, the novel regulation is effected both inprocess stage (I) and in process stage (III).

[0116] Of course, this embodiment of process II also comprisesprocedures in which, in at least one additional process stage in afurther reaction space in the presence of a further catalyst, which maybe identical to or different from the catalysts used in (I) and (III),by regulation of the temperature profile in the reaction space and, ifrequired, additionally through the molar ratio of ammonia to alkyleneoxide, the product selectivity in this at least one additional processstage can be changed in comparison with the second or generally with therespective preceding process stage.

[0117] Further possibilities for influencing the distribution of thealkanolamines in the product spectrum, in addition to the novelregulation of the temperature profile by additional measures, forexample the molar ratios of the starting materials of the individualprocess stages, pressure or residence times of reactants in reactionspaces, are described above and can also be used in process II describedhere.

[0118] This procedure can be carried out essentially for all alkyleneoxides which are described above and can be used as starting materials.A preferably used starting material for the purposes of the presentinvention is ethylene oxide.

[0119] The present invention therefore also relates to a process II, asdescribed above, wherein

[0120] (I) monoethanolamine is selectively prepared by reacting ammoniawith ethylene oxide in a first process stage in a first reaction spacein the presence of a first catalyst, a mixture comprisingmonoethanolamine being obtained,

[0121] (II) monoethanolamine is separated, in a separation stage, fromthe mixture obtained from (I), and

[0122] (III) diethanolamine is selectively obtained in a second processstage by reacting the monoethanolamine obtained from (II) with ethyleneoxide in a second reaction space in the presence of a second catalyst.

[0123] Regarding the catalysts which are used in (I) and (III), thesemay be identical to or different from one another. Regarding thecatalysts which can be used in principle and preferably, reference maybe made to the above description.

[0124] In this embodiment of the novel process II, monoalkanolamines aregenerally prepared at pressures which are from 20 to 250, preferablyfrom 40 to 230, particularly preferably from 70 to 160, bar. Thetemperature of the ammonia stream and the temperature of the alkyleneoxide stream, which are passed into the reaction space, are in generalfrom 20 to 200° C., preferably from 50 to 150° C., particularlypreferably from 60 to 140° C. The molar ratio of ammonia to alkyleneoxide is in general from 100 to 7, preferably from 40 to 7, particularlypreferably from 20 to 7. The maximum temperature in the reaction spaceis furthermore generally less than 200° C., preferably from 20 to 180°C., more preferably from 50 to 150° C., particularly preferably from 60to 130° C.

[0125] The isolation of the monoalkanolamine according to (II) can becarried out by all suitable processes II. Preferably, components of themixture obtained from (I) which are low-boiling in comparison withmonoalkanolamine are first separated off and then the monoalkanolamineis isolated. All separations here are preferably effected bydistillation. The low-boiling components separated off, for exampleammonia or water, can be recycled after the separation to (I).

[0126] The particularly preferred monoethanolamine is isolated from themixture, obtained from (I), by distillation or rectification methods.

[0127] In the second reaction stage (III), the monoalkanolamine obtainedfrom (II) is reacted with alkylene oxide. In the novel process II, thisreaction is effected at pressures which are in general from 20 to 250,preferably from 40 to 230, particularly preferably from 70 to 160, bar.The temperature of the monoalkanolamine stream and the temperature ofthe alkylene oxide stream, which are passed into the second reactionspace, are in general from 20 to 180° C., preferably from 40 to 150° C.,particularly preferably from 60 to 140° C. The molar ratio ofmonoalkanolamine to alkylene oxide here is in general from 10 to 2,preferably from 8 to 2, particularly preferably from 7 to 2. The maximumtemperature in the reaction space is furthermore generally from 70 to200° C., more preferably from 75 to 150° C., particularly preferablyfrom 80 to 140° C.

[0128] In a preferred embodiment, monoalkanolamine is preparedselectively in (I) and dialkanolamine is prepared selectively in (III).In this preferred embodiment of the novel process II, the termselectivity is used as follows:

[0129] the desired product monoalkanolamine is prepared selectively in(I) when more than 70% by weight of monoalkanolamine are present in theproduct spectrum and

[0130] the desired product dialkanolamine is prepared selectively in(III) when the weight ratio of diethanolamine to triethanolamine in thedischarge is ≧2.5.

[0131] The data in % by weight are based in each case on the totalamount of the alkanolamines prepared in (I) and in (III).

[0132] The present invention accordingly also relates to a process II,as described above, wherein

[0133] (A) more than 70% by weight of monoethanolamine are formed in (I)and

[0134] (B) the weight ratio of diethanolamine to triethanolamine in thedischarge is ≧2.5 in (III),

[0135] based in each case on the total amount of mono-, di- andtriethanolamine in the product spectrum of the respective process stage.

[0136] If, in the novel process II, monoethanolamine is preparedselectively in a first process stage, selectivity being understood asthat defined in (A), in general pressures of from 20 to 250, preferablyfrom 40 to 230, particularly preferably from 70 to 160, bar areemployed. The residence times of the reaction medium in the reactor arein general from 2 to 60, preferably from 5 to 20, minutes. The molarratio of ammonia to ethylene oxide is in general from 5 to 100,preferably from 5 to 40, more preferably from 5 to 20, mol. Here,temperature gradients, i.e. temperature differences, between the maximumtemperature in the reaction space and the temperature of the unmixedstarting materials are employed, which are in general from 0 to 100° C.,preferably from 0 to 80° C., more preferably from 0 to 30° C.

[0137] If diethanolamine is prepared selectively in a second processstage in a second reaction space in the presence of a second catalyst,selectivity being understood as meaning that defined in (B), in generalpressures of from 20 to 150, particularly preferably from 30 to 80, barare employed. The residence times of the reaction medium in the reactorare in general from 1 to 60, particularly preferably from 1 to 30, inparticular from 2 to 10, minutes. The molar ratio of ammonia to ethyleneoxide is in general from 20 to 3, preferably from 16 to 4, in particularfrom 10 to 4.

[0138] Here, temperature gradients, i.e. temperature differences,between the maximum temperature in the reaction space and thetemperature of the unmixed starting materials are employed, which are ingeneral from 0 to 150° C., preferably from 0 to 70° C., more preferablyfrom 0 to 40° C.

[0139] The statements made above regarding pressure, temperature andresidence time relate to embodiments of the novel process II which arecarried out in tubular reactors or in cascades of stirred kettlesthrough which the flow is continuous, it being possible for theseparameters to be adapted by a person skilled in the art by means ofroutine tests when other reactors are used.

[0140] The dialkanolamine obtained in (III) can be isolated from theproduct mixture, obtained in (III), by any suitable methods. Preferably,this separation is effected by distillation.

[0141] If monoalkanolamine is present in the product spectrum from(III), it can be recycled as starting material to (III) in a preferredembodiment.

[0142] The Examples which follow illustrate the invention.

EXAMPLES Example 1 Preparation of catalyst 1

[0143] 400 g of pentasil zeolite having the structure ZBM-10, preparedaccording to DE-A 43 23 774.6, was milled using an Alexander unit ofsieve mesh size 1 mm.

[0144] The milled catalyst was then kneaded together with 100 g ofPlural® from Condea and 10 g of formic acid, 400 ml of water beingadded. After a kneading time of 60 minutes, a further 100 ml of waterwere added.

[0145] After a total kneading time of 75 minutes, the kneaded materialwas processed in an extruder at 50 bar to give 3 mm extrudates.

[0146] The material obtained was then dried for 16 hours at 120° C. andthen calcined for 5 hours at 500° C. under air.

Example 2 Preparation of Catalyst 2

[0147] 16 g of 3-aminopropyltriethoxysilane were dissolved in 1000 ml ofanhydrous ethanol, which was predried over a 3 Angstrom molecular sieve,and 100 g of the catalyst according to Example 1 were added in a flask.

[0148] The batch was thoroughly mixed at a low speed for 10 hours in arotary evaporator. The solvent was then evaporated.

[0149] The material obtained was heated to 550° C. at a heating rate of2° C./min and was calcined for 3 hours at 550° C. under air.

Example 3 Preparation of Catalyst 3

[0150] This Example corresponds to reference example 3 of EP-A 0 941986, which is hereby incorporated by reference in the context of thepresent application.

Example 4 Preparation of Catalyst 4 (La/Montmorillonite)

[0151] This Example corresponds to catalyst E of EP-A 0 652 207, whichis hereby incorporated by reference in the context of the presentapplication.

Examples 5 to 7 Preparation of Ethanolamines

[0152] The feed temperature of the ammonia stream was 70° C. Thetemperature of the ethylene oxide stream was 25° C. The temperaturegradient was chosen so that the steepest temperature rise occurred inthe first reactor section comprising 5% of the reaction zone (identicalto 5% of the reaction volume). The temperatures in the downstreamtubular reactor system comprising from 2 to 7 independently thermostatedtube sections were kept constant at desired temperatures of from 90 to160° C., which were uniform in the individual experiments.

[0153] The temperature regulation was effected as described above byadapting the inlet temperature of the individual coolant stream. Thetemperature was measured at the mixing point and with two thermocoupleseach in each tube section in the interior of the reaction tube, and theinlet and outlet temperatures of the cooling medium in the doublejackets of the tube sections were additionally measured.

[0154] Ethylene oxide and ammonia were passed through a tubular reactorhaving an internal diameter of 4 mm and a length of 3 m at from 110 to120 bar, the residence time being about 3.3 minutes. The residence timeswere calculated on the basis of the densities of pure ethylene oxide andpure ammonia under reaction conditions and are based on the volume ofthe empty tube.

[0155] Here, the tubular reactor was filled in each case with 15 g ofthe catalysts stated in Table 1.

[0156] The temperature of the reactor was established by means of athermostated oil circulation through a double jacket around the reactiontube.

[0157] The reaction discharge was analyzed by gas chromatography, thecompositions stated in Table 1 being determined. TABLE 1 Selectivities/Molar ratio Temp./ % by weight Example Catalyst NH₃/EO ° C. MEA DEA TEA5 1 10 90 71 28  1 6 1  4 90 42 40 17 7 1 10 160  26 28 46

[0158] The abbreviations EO, MEA, DEA and TEA represent ethylene oxide,monoethanolamine, diethanolamine and triethanolamine. The selectivity isdefined as % by weight of alkanolamine/% by weight of the ethanolaminesformed in total.

Example 8 Flexible Preparation of Ethanolamines

[0159] This Example was carried out analogously to Examples 5 to 7, amixture of water and 15% of ammonia being used instead of a catalyst.TABLE 2 Selectivities/ Molar ratio Temp./ % by weight Example CatalystNH₃/EO ° C. MEA DEA TEA 11 Water, 15% 6  90 70 23  7 12 Water, 15% 6 13038 37 25 13 Water, 15% 6 170 17 28 55

Examples 9 to 13 Selective Preparation of Diethanolamine

[0160] (a) Selective Preparation of Monoethanolamine

[0161] Ethylene oxide and ammonia were passed through a tubular reactorhaving an internal diameter of 4 mm and a length of 3 m at from 110 to120 bar, the residence time being about 3.3 minutes. The residence timeswere calculated on the basis of the densities of pure ethylene oxide andpure ammonia under reaction conditions and are based on the volume ofthe empty tube.

[0162] Here, the tubular reactor was filled in each case with 15 g ofthe catalysts stated in Table 2.

[0163] The temperature of the reactor was established by means of athermostated oil circulation through a double jacket around the reactiontube, the feed temperature being 70° C.

[0164] The reaction discharge was analyzed by gas chromatography, thecompositions stated in Table 3 being determined. TABLE 3 Selectivities/Exam- Molar ratio Temp./ % ple Catalyst NH₃/EO ° C. MEA DEA TEA  9Dowex ® 50X8 60 100 92  8 0 10 4 25  95 90 10 0 C1 15% by wt. of 10 10060 30 10  water

[0165] Water was added to the ammonia stream to give a waterconcentration of 15% by weight in the water-containing ammonia stream.In the further examples, in which the presence of water in the feed wasnot expressly referred to, anhydrous ammonia was used.

[0166] The abbreviations EO, MEA, DEA and TEA represent ethylene oxide,monoethanolamine, diethanolamine and triethanolamine. The selectivity isdefined as the ratio of the percentages by weight of the alkanolaminesto the sum of the percentages by weight of the ethanolamines formed.

[0167] (b) Selective Preparation of Diethanolamine

[0168] Monoethanolamine was reacted with ethylene oxide over a fixed bedin the tubular reactor. The reaction was carried out as in Examples 9 to13 (a).

[0169] The reaction discharge was analyzed by gas chromatography, thecompositions stated in Table 4 being determined. TABLE 4 Molar ratioTemp./ Selectivities/% Example Catalyst MEA/EO ° C. DEA TEA 11 3 4 11090 10 C2 Autocatalysis 4 110 86 14

[0170] The Comparative Example denoted by C2 was carried out withoutaddition of a catalyst.

[0171] (c) Combination of the Processes for Selective MEA SynthesisAccording to (a) with the Process for the Selective Preparation ofDiethanolamine According to (b)

[0172] Table 5 shows the results of experiments which were achieved in acombination process using two reactors. TABLE 5 Temp./ Exam- ° C.Selectivities ple Catalyst I Catalyst II Reactor 1/2 DEA TEA 12 Dowex ®50X8 3 100/110 91 9 13 4 3  95/110 91 9 C3 Dowex ® 50X8 Autocatalysis110/110 87 13 

We claim:
 1. A process for the preparation of at least one alkanolamineby reacting ammonia with alkylene oxide in a reaction space in thepresence of a catalyst to give monoalkanolamine or dialkanolamine ortrialkanolamine or a mixture of two or three of these compounds, thedistribution of the various alkanolamines in the product spectrum beingcontrolled by means of the temperature in the reaction space, whereinthe temperature is established by regulating the temperature profile inthe reaction space.
 2. A process as claimed in claim 1, wherein theregulation of the temperature profile in the reaction space is effectedby determining the temperature gradient in the reaction space or bydetermining the location of the maximum temperature in the reactionspace or by determining both parameters.
 3. A process as claimed inclaim 1 or 2, wherein the distribution of the various alkanolamines inthe product spectrum is additionally controlled through the molar ratioof ammonia to alkylene oxide.
 4. A process as claimed in any of claims 1to 3, wherein the reaction is carried out in a tubular reactor.
 5. Aprocess as claimed in any of claims 1 to 4, wherein the reaction iscarried out in the presence of a heterogeneous catalyst, preferably of aheterogeneous zeolite catalyst.
 6. A process as claimed in claim 5,wherein the catalyst is a silylated zeolite catalyst.
 7. A process asclaimed in any of claims 1 to 6, wherein the alkylene oxide used isethylene oxide.
 8. A process as claimed in claim 7, wherein (i) in afirst process stage, monoethanolamine or diethanolamine ortriethanolamine with high selectivity is prepared and (ii) in a secondprocess stage, in the same reaction space and in the presence of thesame catalyst, by regulation of the temperature profile in the reactionspace, the product selectivity in the second process stage is changed incomparison with the first process stage.
 9. A process as claimed inclaim 8, wherein (a) more than 65% by weight of monoethanolamine areformed in (i) and more than 35% by weight of di- or triethanolamine areformed in (ii) or (b) more than 35% by weight of di- or triethanolamineare formed in (i) and more than 65% by weight of monoethanolamine areformed in (ii), based in each case on the total amount of mono-, di- andtriethanolamine.
 10. A process as claimed in claim 7, wherein (I)monoethanolamine is prepared with high selectivity by reacting ammoniawith ethylene oxide in a first process stage in a first reaction spacein the presence of a first catalyst, a mixture comprisingmonoethanolamine being obtained, (II) monoethanolamine is separated, ina separation stage, from the mixture obtained from (I), and (III)diethanolamine with high selectivity is obtained in a second processstage by reacting the monoethanolamine obtained from (II) with ethyleneoxide in a second reaction space in the presence of a second catalyst.11. A process as claimed in claim 10, wherein (A) more than 70% byweight, based on the total amount of mono-, di- and triethanolamine inthe product spectrum, of monoethanolamine are formed in (I) and (B) theweight ratio of diethanolamine to triethanolamine in the discharge is≧2.5 in (III).
 12. A process as claimed in any of claims 1 to 11,wherein the alkylene oxide is prepared by reacting an alkene with ahydroperoxide, an oxygen-containing gas or pure oxygen.